Method and system for encoding packet interdependency in a packet data transmission system

ABSTRACT

Method and system for encoding packet interdependency in a packet data stream. In one embodiment, the scheme comprises providing, for each packet in the packet data stream, a dependency relationship field associated therewith; and representing dependency of a first packet on a second packet of the packet data stream by a binary code in the dependency relationship field of the first packet, the binary code for describing the dependency as a subset relationship between the first and second packets.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made under the support of the United StatesGovernment, Department of Commerce, National Institute of Standards andTechnology (NIST), Award Number 70NANB3H3053. The United StatesGovernment has certain rights in the invention.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention generally relates to packet data transmission.More particularly, and not by way of any limitation, the presentinvention is directed to a method and system for encoding packetinterdependency in a packet data transmission system.

2. Description of Related Art

In some packet data transmission systems, packets carrying data exhibitinterdependency, e.g., packets relating to compressed video sequences,where some packets of the data stream have payloads that depend on thecontents of other packets in a sequence. While allowing suchinterdependency is useful in bandwidth management, it does give rise tocertain issues that must be addressed. For instance, if it is necessaryto drop packets at a point in the transmission system (due tocongestion, as an example), it becomes important to have some knowledgeof the packet interdependency so that packets on which other packetsdepend are not preferred for dropping.

SUMMARY OF THE INVENTION

In one aspect, a scheme is disclosed for encoding packet interdependencyin a packet data stream using a compact encoding mechanism. In oneembodiment, the scheme comprises providing, for each packet in thepacket data stream, a dependency relationship field (DRF) associatedtherewith; and representing dependency of a first packet on a secondpacket of the packet data stream by a binary code in the dependencyrelationship field of the first packet, the binary code for describingthe dependency as a subset relationship between the first and secondpackets.

In another embodiment, the scheme comprises providing, for each packetin the packet data stream, a relative displacement pointer (RDP) fieldassociated therewith, the RDP field including a first directiondependency subfield and a second direction dependency subfield; andrepresenting dependency of a particular packet of the packet data streamby a first binary code in the first direction dependency subfield and asecond binary code in the second direction dependency subfield, thefirst binary code for describing the particular packet's dependency on apacket disposed in one direction of the packet data stream and thesecond binary code for describing the particular packet's dependency ona packet disposed in an opposite direction of the packet data stream.

In a further embodiment, the present invention is directed to a systemfor encoding packet interdependency in a packet data stream, comprising:means for providing, for each packet in the packet data stream, a DRFportion associated therewith; and means for representing dependency of afirst packet on a second packet of the packet data stream by a binarycode in the dependency relationship field of the first packet, thebinary code for describing the dependency as a subset relationshipbetween the first and second packets.

In a still further embodiment, the present invention is directed to asystem for encoding packet interdependency in a packet data stream,comprising: means for providing, for each packet in the packet datastream, an RDP field associated therewith, the RDP field including afirst direction dependency subfield and a second direction dependencysubfield; and means for representing dependency of a particular packetof the packet data stream by a first binary code in the first directiondependency subfield and a second binary code in the second directiondependency subfield, the first binary code for describing the particularpacket's dependency on a packet disposed in one direction of the packetdata stream and the second binary code for describing the particularpacket's dependency on a packet disposed in an opposite direction of thepacket data stream.

In another aspect, a packet data transmission system for transmitting apacket data stream is disclosed. In one embodiment, the packet datatransmission system comprises: a packet data transmitter operable tomultiplex data from a plurality of video sources into the packet datastream; an encoder for representing dependency of a first packet on asecond packet of the packet data stream by a binary code in a dependencyrelationship field of the first packet, the binary code for describingthe dependency as a subset relationship between the first and secondpackets; and a packet data receiver including a decoder for receivingthe packet data stream, the decoder for decoding dependency of packetsin the packet data stream.

In another embodiment, the packet data transmission system of thepresent invention comprises: a packet data transmitter operable tomultiplex data from a plurality of video sources into the packet datastream; an encoder for representing dependency of a particular packet ofthe packet data stream by a first binary code in the first directiondependency subfield and a second binary code in the second directiondependency subfield, the first binary code for describing the particularpacket's dependency on a packet disposed in one direction of the packetdata stream and the second binary code for describing the particularpacket's dependency on a packet disposed in an opposite direction of thepacket data stream; and a packet data receiver including a decoder forreceiving the packet data stream, the decoder for decoding dependency ofpackets in the packet data stream.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated into and form a part of thespecification to illustrate one or more presently preferred exemplaryembodiments of the present invention. Various advantages and features ofthe invention will be understood from the following Detailed Descriptiontaken in connection with the appended claims and with reference to theattached drawing figures in which:

FIG. 1 depicts an exemplary packet data transmission system wherein anembodiment of the present invention may be practiced;

FIG. 2 depicts an exemplary packet data sequence operable in the packetdata transmission system of FIG. 1;

FIG. 3 depicts an embodiment of a packet interdependency encoding schemein accordance with the teachings of the present invention;

FIG. 4 depicts an illustration of the packet interdependency encodingscheme of FIG. 3;

FIG. 5 depicts an exemplary packet data transmission system whereinanother embodiment of the present invention may be practiced;

FIG. 6 depicts an embodiment of a relative displacement pointer (RDP)field for encoding packet interdependency in accordance with theteachings of the present invention;

FIG. 7 depicts an illustration of the packet interdependency encodingscheme using the RDP field;

FIGS. 8A and 8B depict an illustration of the transitive property of thepacket interdependency relationship; and

FIGS. 9A and 9B are flowcharts associated with the embodiments of thepresent invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference tovarious examples of how the invention can best be made and used. Likereference numerals are used throughout the description and several viewsof the drawings to indicate like or corresponding parts, wherein thevarious elements are not necessarily drawn to scale. Referring now tothe drawings, and more particularly to FIG. 1, depicted therein is anexemplary packet data transmission system 100 wherein an embodiment ofthe present invention may be practiced for purposes of encodinginter-packet dependency relationships that may exist between datapackets. By way of illustration, the packet data transmission system 100may comprise any generalized transmission system that involvesgeneration, transmission and reception of packetized data wherein packetinterdependency exists. For instance, as alluded to in the Backgroundsection of the present patent disclosure, packets carrying data relatingto compressed video sequences have a dependency relationship becausesome packets contain data that depend on the contents of other packetsin a sequence. Accordingly, the packet data transmission system 100 maycomprise a compressed video transmission system in one exemplaryembodiment, although it will be apparent that the teachings of thepresent invention may be practiced in other packet data transmissionsystems as well.

As illustrated, the packet data transmission system 100 includes aplurality of data sources, e.g., Source-1 102-1 through Source-N 102-N,that generate data packets for transmission. A packet data transmitter104 is operable to multiplex the packet data from the N independentsources so that the merged data can be transported on a single, sharedlink 110 for reception by a packet data receiver 108. An encoder 106associated with the packet data transmitter 104 is operable to providean inter-packet dependency relationship encoding mechanism wherein eachpacket is provided with a dependency relationship field (DRF) as will beset forth in detail hereinbelow. Those skilled in the art will recognizethat although the encoder 106 is shown as a separate block in FIG. 1, itmay be integrated within the packet data transmitter 104. Furthermore,the encoder may be disposed further upstream in the transmission system100 such that the independent streams of data from each data source isencoded appropriately before it is multiplexed for transmission.Regardless of how encoding is effectuated at the source side of thepacket data transmission system 100, a decoder 110 is associated withthe packet data receiver 108 that is operable to decode the encodedpacket data so as to determine appropriate inter-packet dependencies ofthe received packets.

FIG. 2 depicts an exemplary packet data sequence 200 operable in thepacket data transmission system 100 of FIG. 1, wherein packetinterdependent relationships may arise. By way of example, the packetdata sequence 200, which may be generated by the packet data transmitter104, is shown to comprise two subsequences, Subsequence A 202A andSubsequence B 202B. Each subsequence in turn includes a plurality ofpackets that may show some degree of interdependency, although packetsin one subsequence are typically not dependent on the packets fromanother subsequence. Subsequence A 202A is illustrated with N packets,A(1) 204-1 through A(N) 204-N, whereas Subsequence B 202B includes Mpackets, B(1) 206-1 through B(M) 206-M. Alternatively, some subsequencesmay have the same number of packets in a data stream.

FIG. 3 depicts an embodiment of a packet interdependency encoding scheme300 in accordance with the teachings of the present invention. By way ofexample, Subsequence A involving N packets is illustrated as a packetdata stream wherein each packet is provided with a DRF of arbitrary size(i.e., a binary field of any size) associated therewith. The startingpacket of the data stream, A(1) 204-1, is provided with a DRF 302-1, thenext packet, A(2) 204-1, is provided with a DRF 302-2, and so on, forthe entire packet data stream. A number of interdependency relationshipsamong the N data packets exist such that the contents of at least onepacket of the data stream depends on the contents of another packettherein. In accordance with the teachings of the present invention,dependency of a first packet in the data stream on a second packettherein is represented by a binary code in the DRF associated with thefirst packet such that the binary code is encoded with a set theoryformulation for describing the dependency as a subset relationshipbetween the first and second packets. Accordingly, as many subsetrelationships are created by the DRF encoding mechanism as there are theinterdependencies among the data packets. As illustrated, Kinterdependent relationships are exemplified, which give rise to Ksubset formulations based on the binary coding of the DRFs of thepackets by the DRF encoding mechanism of the present disclosure.

In terms of implementation, the DRFs may be provided within a headerblock of each of the data packets, which may thereby require somemodification to the packet data protocol being used by the packet datatransmission system. Alternatively, the DRFs may be provided within apayload portion of the data packets so long as the transmission systemis capable of treating the DRFs appropriately for purposes of decodingthe packet interdependencies and not as part of the data itself.

FIG. 4 depicts an illustration of the packet interdependency encodingscheme of FIG. 3. Reference numeral 400 refers to a stream of six datapackets, packet A 402-A through packet F 402-F, each having a 5-bit DRFthat is appropriately encoded to describe the interdependencies in thepacket data. Accordingly, reference numerals 404-A through 404-F referto the DRFs associated with the six data packets, respectively. Further,six interdependent relationships are exemplified: packet B depends onpacket A as well as on packet C; packet C in turn depends on packet A aswell as on packet D; and both packet E and packet F depend on packet D.As illustrated, these six interdependent relationships are shown byrespective directional arrows 406-1 through 406-6.

In one embodiment, the most significant bit (MSB) of the DRF of thestarting packet may be set in order to indicate the beginning of asubsequence within which one or more interdependent relationships mayexist. In other words, setting the MSB of the DRF of the starting packetallows demarcation of a group of packets which need to be encodedappropriately based on any interdependencies therein. As shown in FIG.4, the MSB of DRF 404-A associated with packet A is set (i.e., MSB=1),thereby indicating the start of the subsequence. The MSBs of the DRFs ofthe remaining packets in the subsequence are all cleared (i.e., MSB=0).The subfields of each DRF (i.e., the bits after the MSB, hereinafterreferred to as the “sub-DRF”) are then encoded in a binary code so thatwhen the full complement of the 5-bit DRFs are provided, they areoperable to represent the interdependencies in a mathematical propersubset formulation. For example, to represent that packet B is dependenton packet A, the sub-DRF of packet B is coded as [1000], whereby its DRFbecomes [01000] which is a proper subset of packet A's DRF 404-A that iscoded with binary code [11100] (i.e., the sub-DRF of packet A isprovided as [1100]). In set theory notation, this relationship isrepresented as BcA, that is, B is a proper subset of A. In FIG. 4,reference numeral 408-1 refers to this subset relationship. Likewise, torepresent that packet B is dependent on packet C, the sub-DRF of packetC is coded as [1100], whereby its DRF becomes [01100]. Thus, the DRF ofpacket B remains a proper subset of the DRF of packet C, while packet Citself is dependent on packet A (since [01100] is a proper subset of[11100], the DRF of packet A). In other words, both BcC and CcArelationships are maintained by appropriately encoding the respectiveDRFs. These subset relationships are labeled as reference numerals 408-2and 408-3, respectively, in FIG. 4. In similar fashion, the DRFs of theremaining packets are encoded by the encoding mechanism of the presentdisclosure as [01110] for packet D, [00010] for packet E, and [00010]for packet F.

It is possible that the DRFs of two packets may be the same but there isno dependency relationship between them. For example, it should be notedthat since the DRFs of packet E and packet F are the same, there is noproper subset relationship. Accordingly, the set theory representationF⊂E (because DRF of E≡DRF of F) is in conformity with the independentrelationship between the two packets.

Those skilled in the art should appreciate that the DRF encodingmechanism set forth above is operable to encode an arbitrary number ofinterdependency relationships in a packet data stream so long asappropriate delimiters are encoded for identifying groups of packetswithin which inter-packet DRF comparisons are to be restricted. In anexemplary application, it would be desirable to impose a rule that astarter packet in a subsequence (such as packet A in the above examplewhere the MSB of the DRF is set) be also operable as a “terminator”packet such that it belongs only to the subsequence it starts.Regardless of how a sequence is delimited, it should be apparent thatthe DRF encoding process starts afresh for each new subsequence.

FIG. 5 depicts an exemplary packet data transmission system 500 whereinanother embodiment of the present invention may be practiced. Similar tothe packet data transmission system 100 of FIG. 1, independent sources102-1 through 102-N provide various streams of packet data formultiplexing by the packet data transmitter 104. As will be explainedbelow, an encoder 502 associated with the transmitter 104 and/or theindependent sources is operable to provide a relative displacementpointer (RDP) field in each packet so that a dependent packet may pointto other packets in a packet data stream. A suitable RDP decoder 504associated with the packet data receiver 108 is operable to decode theencoded packet data so as to determine appropriate inter-packetdependencies of the received packets.

FIG. 6 depicts an embodiment of a relative displacement pointer (RDP)field of arbitrary size for encoding packet interdependency inaccordance with the teachings of the present invention. Referencenumeral 600 refers to a generalized RDP-encoded packet which includes apayload block 602 and an RDP field 604. In the exemplary embodimentdepicted, the RDP field 604 is shown as a field that is separate fromthe payload block 602, possibly placed within a header block (notexplicitly shown). In other embodiments, however, the RDP field 604 maybe provided elsewhere within the generalized data packet 600. Regardlessof where it is placed, the RDP field 604 is comprised of a “Start”subfield 606, a first direction dependency subfield 608, and a seconddirection dependency subfield 610, wherein each subfield may include anappropriate number of bits. In one implementation, the RDP encodingmechanism of the present disclosure may encode the Start subfield 606 ofa beginning packet with a single bit that is set (i.e., Start=1) inorder to encode a group of related packets that follow the beginningpacket. All other packets in the group may be coded with Start=0. Thefirst direction dependency subfield 608 of the packet is coded with afirst binary code for describing the packet's dependency on a packetdisposed in one direction of the packet data stream (e.g., backward orforward with respect to the packet under consideration). Likewise, thesecond direction dependency subfield 610 of the packet is coded with asecond binary code for describing the packet's dependency on a packetdisposed in the other direction of the packet data stream (i.e., in adirection opposite to the direction identified by the first directiondependency subfield 608).

By way of implementation, essentially, the directional dependencysubfields 608, 610 are coded with the binary numbers that arerepresentative of the relative distance between a dependent packet andthe packet it depends on, in either direction, thereby identifying theupstream packet as well as the downstream packet on which the dependentpacket depends. It should be realized that although both first andsecond direction dependency subfields 608 and 610 may be provided withthe same number of bits (i.e., the same size) in an exemplaryimplementation, there is no such limitation for purposes of the presentpatent application. Further, the size of the directional dependencysubfields may vary depending on how large a pointer in either directionis to be implemented in a particular application given the constraintsof protocol overhead, complexity, computational expense, etc.

FIG. 7 depicts an illustration of the packet interdependency encodingscheme using the RDP field embodiment described above. Reference numeral700 refers to a packet data stream including six packets, packet A 702-Athrough packet F 702-F, each having a 5-bit RDP field that isappropriately encoded to describe the bidirectional interdependencies inthe packet data. Accordingly, reference numerals 704-A through 704-Frefer to the RDP fields associated with the six data packets,respectively. Further, similar to the illustrative data stream 400 shownin FIG. 4, the same six interdependent relationships are exemplified:packet B depends on packet A as well as on packet C; packet C in turndepends on packet A as well as on packet D; and both packet E and packetF depend on packet D. Packet A 702-A has its 5-bit RDP field 704-A codedwith [10000], indicating that it is the beginning packet of asubsequence (since its MSB=1). Additionally, both its first and seconddirectional dependency subfields are [00], thereby signifying thatpacket A is not dependent on any other packet in either direction.Packet B 702-B has its RDP field 704-B coded with [00101]; that is, itsStart subfield 712=[0], first direction dependency subfield 714=[01] andsecond direction dependency subfield 716=[01]. Accordingly, packet B702-B is dependent on one packet to its left (i.e., packet A) and onepacket to its right (i.e., packet C). Based on whatever convention isapplied for signifying direction, these packets are upstream ordownstream (or, forward or backward) from the standpoint of packet B.Likewise, packet C 702-C has its RDP field 704-C coded with [01001] suchthat its Start subfield 706=[0], first direction dependency subfield708=[10] (signifying packet C's dependency on a packet that is disposedtwo packets from itself) and second direction dependency subfield710=[01] (signifying packet C's dependency on a packet that is disposedone packet away). As illustrated, these packets are packets A and D,respectively. In similar fashion, the RDP encoding mechanism of thepresent invention provides the RDP subfields of packet D, packet E andpacket F as [00000] (signifying that packet D is not dependent, nor isit a starting packet), [00100] (signifying that packet E is dependent ofpacket D), and [01000] (signifying that packet F is dependent on packetD), respectively.

It should be noted that in the exemplary RDP field encoding scheme setforth above, only five bits are used, which limits a directionaldisplacement pointer to point to at most three packets in each direction([00]=no dependency; [01]=one packet away; [10]=two packets away; and[11]=three packets away). This range can be exceeded by making use ofthe transitive property of the dependency relationship as illustrated inFIGS. 8A and 8B. In FIG. 8A, reference numeral 800A refers to afive-packet subsequence, packet A 802-A through packet E 802-E, eachhaving a 5-bit RDP field 804-A through 804-E. Four dependencyrelationships 808-1 through 808-4 are illustrated: each of packets B, C,D and E depends only on packet A. Whereas the 5-bit RDP fields 804-Bthrough 804-D are adequate to describe the dependencies of packets B, Cand D (on packet A), the dependency of packet E on packet A cannot bedescribed using this pointer because the relative displacement exceeds3. In FIG. 8B, the coding makes use of the transitive property of thedependencies, wherein reference numeral 800B refers to the five-packetsubsequence with packet interdependencies being resolved such that adependent packet depends on a packet that is at most only one packetaway. Using the transitive property to represent that packet Eultimately depends on packet A because it depends of packet D, which inturn depends on packet C, which depends on packet B, which in turndepends on packet A, a new set of dependencies 810-1 through 810-4 areobtained. Likewise, the 3-packet-long dependency of packet D on packet Acan be broken into a number of 1-packet-long dependencies (throughpackets C, B and ultimately A). In other words, the “long distance”parallel dependencies are resolved into a number of “short distance”serial dependencies by using the transitive property of therelationships. Since each of these dependencies describe displacementsof only one packet, the 5-bit RDP fields 806-A through 806-E of thepackets can be coded appropriately to represent these dependencyrelationships.

Referring now to FIGS. 9A and 9B, shown therein are two flowchartsassociated with the embodiments of the present invention. In FIG. 9A,the flowchart describes the operations involved in a DRF encoding schemefor describing the interdependency in a packet data stream. For eachpacket in the packet data stream, a DRF portion is provided by anencoder disposed in a packet data transmission system (block 902). Asalluded to in the foregoing description, the DRF portion may occupy aportion of the packet headers or be disposed within the payload of thepackets. The encoder is operable to represent dependency of a firstpacket on a second packet of the data stream (e.g., a subsequence or agroup of related packets) by a binary code in the DRF portion, whereinthe binary code describes the dependency based on a set theoryformulation, i.e., as a subset relationship between the first and secondpackets (block 904).

In FIG. 9B, the flowchart describes the operations involved in an RDPfield encoding scheme for describing the interdependency in a packetdata stream. For each packet in the packet data stream, an RDP field isprovided by an encoder disposed in a packet data transmission system,wherein the RDP field is comprised of a first direction dependencysubfield and a second direction dependency subfield (block 920). Asexplained elsewhere in the present disclosure, the RDP field may occupya portion of the packet headers or be disposed within the payload of thepackets. The encoder is operable to represent dependency of a particularpacket of the data stream (e.g., a subsequence or a group of relatedpackets) by a first binary code in the first direction dependencysubfield and a second binary code in the second direction dependencysubfield, wherein the first binary code is for describing the particularpacket's dependency on a packet disposed in one direction of the datastream and the second binary code is for describing the particularpacket's dependency on a packet disposed in an opposite direction of thedata stream (block 922).

Based on the foregoing Detailed Description, it should be appreciatedthat the exemplary embodiments of the present invention advantageouslyprovide a compact signaling mechanism for describing packetinterdependencies in a packet data transmission system. Accordingly, theembodiments described herein provide a data stream traffic managerdisposed in the packet data transmission system the requisiteinformation that allows it to manage and possibly avoid unnecessarypacket data loss (due to a congestion management policy, for example) inan intelligent manner. In particular, if it is necessary to drop one oftwo packets to resolve congestion and if one of the packets depends onthe other, then the manager can drop the dependent packet, sincedropping the independent packet would render the dependent packetunusable. Further, the compact aspect of the embodiments set forthherein allows packet interdependency information to be signaled to thetraffic manager without the use of additional “out-of-band” signalingpackets, thereby minimizing protocol overhead, computational complexity,et cetera.

Although the invention has been described with reference to certainexemplary embodiments, it is to be understood that the forms of theinvention shown and described are to be treated as exemplary embodimentsonly. Accordingly, various changes, substitutions and modifications canbe realized without departing from the spirit and scope of the inventionas defined by the appended claims.

1. A method of encoding packet interdependency in a packet data stream,comprising: generating, via a plurality of data sources, a packet datastream through a video packet data transmitter, wherein the packet datastream comprises a plurality of data packets, each data packet carryingvideo data as payload; for each packet in said packet data stream,providing a relative displacement pointer (RDP) field associatedtherewith, said RDP field including a first direction dependencysubfield and a second direction dependency subfield; representingdependency of a particular packet of said packet data stream by a firstbinary code in said first direction dependency subfield and a secondbinary code in said second direction dependency subfield, said firstbinary code for describing said particular packet's dependency on apacket disposed in one direction of said packet data stream and saidsecond binary code for describing said particular packet's dependency ona packet disposed in an opposite direction of said packet data stream;and receiving said packet data stream by binary code for describing saidparticular packet's dependency on a packet disposed in one direction ofsaid packet data stream and said second binary code for describing saidparticular packet's dependency on a packet disposed in an oppositedirection of said packet data stream in a packet data receivercommunicably coupled to the video packet data transmitter.
 2. The methodof encoding packet interdependency in a packet data stream as recited inclaim 1, wherein said RDP field is provided within a header block ofsaid particular packet.
 3. The method of encoding packet interdependencyin a packet data stream as recited in claim 1, wherein said RDP field isprovided within a payload block of said particular packet.
 4. The methodof encoding packet interdependency in a packet data stream as recited inclaim 1, wherein said RDP field is encoded by an encoder coupled to avideo packet data transmitter.
 5. The method of encoding packetinterdependency in a packet data stream as recited in claim 4, whereinsaid video packet data transmitter functions to multiplex data from aplurality of video sources.
 6. A system for encoding packetinterdependency in a packet data stream, comprising: means for providinga relative displacement pointer (RDP) field associated with each packetin said packet data stream, wherein each data packet carries video dataas payload, said RDP field including a first direction dependencysubfield and a second direction dependency subfield; and means forrepresenting dependency of a particular packet of said packet datastream by a first binary code in said first direction dependencysubfield and a second binary code in said second direction dependencysubfield, said first binary code for describing said particular packet'sdependency on a packet disposed in one direction of said packet datastream and said second binary code for describing said particularpacket's dependency on a packet disposed in an opposite direction ofsaid packet data stream.
 7. The system for encoding packetinterdependency in a packet data stream as recited in claim 6, whereinsaid RDP field is provided within a header block of said first packet.8. The system for encoding packet interdependency in a packet datastream as recited in claim 6, wherein said RDP field is provided withina payload block of said first packet.
 9. The system for encoding packetinterdependency in a packet data stream as recited in claim 6, whereinsaid RDP field is encoded by an encoder coupled to a video packet datatransmitter.
 10. The system for encoding packet interdependency in apacket data stream as recited in claim 9, wherein said video packet datatransmitter functions to multiplex data from a plurality of videosources.
 11. A packet data transmission system for transmitting a packetdata stream, comprising: a packet data transmitter operable to multiplexdata from a plurality of video sources into said packet data stream,wherein the packet data stream comprises a plurality of data packets,each data packet carrying video data as payload; an encoder forrepresenting dependency of a particular packet of said packet datastream by a first binary code in said first direction dependencysubfield and a second binary code in said second direction dependencysubfield, said first binary code for describing said particular packet'sdependency on a packet disposed in one direction of said packet datastream and said second binary code for describing said particularpacket's dependency on a packet disposed in an opposite direction ofsaid packet data stream; and a packet data receiver including a decoderfor receiving said packet data stream, said decoder for decodingdependency of packets in said packet data stream.
 12. The packet datatransmission system for transmitting a packet data stream as recited inclaim 11, wherein said RDP field is provided within a header block ofsaid particular packet.
 13. The packet data transmission system fortransmitting a packet data stream as recited in claim 11, wherein saidRDP field is provided within a payload block of said particular packet.